@Zilly Consider modifying your profile and setting your location to BFE, Canada or whatever you consider appropriate. It'll be good for people to know you're not in the USA when considering your budget and available speakers. Shipping for the AA monitors will likely exceed $100 across the border.
With room dimensions of 18' * 17' * 19', that puts your room at over 5800 cubic feet,
solidly into the Extreme room size category. You really don't have a high enough budget devoted to your subwoofage. If you get the BIC and you're underwhelmed, consider sticking with the towers you already have and putting your entire $950 CAD budget into getting a more capable subwoofer. And even that might not be enough.
The
SVS PC12-NSD would be better, and *might* be the lowest common denominator capable of pressurizing such a large space for less than a grand in Canada, if such a thing exists. That room really needs at least a 15" subwoofer though,
something like the Hsu VTF-15H. If you could save for a Funk Audio sub, that'd be best, and you'd own a piece of true Canadian artisan audiophilia.
Re: towers vs. bookshelfs, that's really more a function of your listening position's linear distance from your mains than the volume of the space. My room is 20' long, and bookshelf speakers are more than plenty. With an appropriate subwoofer, the bass extension achieved by towers instead of bookshelf speakers is rendered moot anyway. The other advantage of towers, higher sensitivity offered by having more drivers, might be a benefit if you had a weaker receiver. But that Yamaha RX-V781 has plenty of power to drive lower sensitivity speakers to satisfactory levels.
